Exemplary embodiments of the invention relate to a rotary wing aircraft, and more particularly, to an assembly for controlling rotor blade pitch of a rotary wing aircraft rotor system.
Control of a rotary wing aircraft is affected by varying the pitch of the rotor blades individually as the rotor rotates, and by varying the pitch of all of the blades together. These are known respectively as cyclic and collective pitch control. Blade pitch control of a rotary wing aircraft main rotor is typically achieved through a swashplate.
The swashplate is typically concentrically mounted about the rotor shaft. The swashplate generally includes two rings connected by a series of bearings with one ring connected to the airframe (stationary swashplate) and the other ring connected to the rotor hub (rotating swashplate). The rotating ring is connected to the rotor hub through a pivoted link device typically referred to as scissors, with the static ring similarly connected to the airframe. The rotating swashplate rotates relative to the stationary swashplate. Apart from rotary motion, the stationary and rotating swashplate otherwise move as a unitary component. Cyclic control is achieved by tilting the swashplate relative to a rotor shaft and collective control is achieved by translating the swashplate along the rotor shaft.
Pitch control rods mounted between the main rotor blades and the rotating swashplate transfer loads between the swashplate and the main rotor blades. Main rotor servos extend between and attach to the stationary swashplate and the aircraft fuselage. Displacement of the main rotor servos results in displacement of the stationary swashplate. Hence, by actuating selected main rotor servos, collective and cyclic commands are transferred to the rotor head as vertical and/or tilting displacement of the swashplates.
Deflection of a swashplate can cause pitch loss at the blades and increased stress in the duplex bearing. To avoid this deflection, swashplates are designed to have a high stiffness, typically by increasing the cross-section of the component; however increasing the cross-section of the swashplate adds weight to the rotary wing aircraft. Although current swashplates perform adequately, it is always desirable to reduce the empty weight of the helicopter. One consideration for decreasing the empty weight of the helicopter is to use a composite material to replace metal components. However, the typical configuration of a swashplate requires tightly toleranced surfaces and interface geometry that are difficult to obtain using composite materials while still maintaining the necessary high strength and acceptable life of the swashplate.